pH Dependency of Kinetic Parameters and Reaction Mechanism of Beef Liver Catalase

Abstract

The pH-dependence of the kinetic parameters in H₂O₂ decomposition by beef liver catalase was investigated. At pH 7.0, the ternary complex (ESS) decomposition rate was about 100 times faster than ESS formation (42μm H₂O₂), and the value of the Michaelis constant was 0.025M.
From ethanol competition experiments, two different proton dissociation constants of the enzyme (pK_e1, =5.0, pK_es2=5.9) were obtained for the binding of first and second H₂O₂ molecules. Another pK_a value (pK_es1) of 4.2 was obtained from the pH dependence of overall rate constant (k₀). The reaction mechanism of catalase was discussed in relation to these ionizable groups.